Hand-held spherical antenna system to detect transponder tagged objects, for example during surgery

ABSTRACT

A hand-held antenna system allows medical personnel to ascertain the presence or absence of objects (e.g., medical supplies) tagged with transponders in an environment in which medical procedures are performed. In use, the hand-held antenna system may be positioned proximate a patient at a time after a medical procedure, such as after child birth, so the system can scan the patient&#39;s body to determine the presence of objects tagged with transponders. The antenna system includes three antenna elements arranged mutually orthogonal to each other to transmit and receive signals in three coordinate directions. A controller is coupled to the antenna elements to transmit signals to the transponders and to receive response signals. The antenna system may operate in a static scan mode wherein the antenna system is held in a fixed position by a user and a dynamic scan mode wherein the antenna system is moved by a user.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation application which claims thebenefit of and priority to U.S. patent application Ser. No. 15/126,726,filed on Sep. 16, 2016, which is a U.S. National Stage Application filedunder 35 U.S.C. § 371(a) of International Patent Application Serial No.PCT/US2014/070547, filed Dec. 16, 2014, which claims the benefit of andpriority to U.S. Provisional Patent Application Ser. No. 61/972,826,filed Mar. 31, 2014, the entire disclosure of which is incorporated byreference herein.

BACKGROUND Field

This disclosure generally relates to the detection of the presence orabsence of objects tagged with transponders, which may, for example,allow the detection of retained medical supplies during medicalprocedures.

Description of the Related Art

It is often useful or important to be able to determine the presence orabsence of an object.

For example, it is important to determine whether objects associatedwith surgery are present in a patient's body before completion of thesurgery. Such objects may take a variety of forms. For example, theobjects may take the form of instruments, for instance scalpels,scissors, forceps, hemostats, and/or clamps. Also for example, theobjects may take the form of related accessories and/or disposableobjects, for instance surgical sponges, gauzes, and/or pads. Failure tolocate an object before closing the patient may require additionalsurgery, and in some instances may have serious adverse medicalconsequences.

Some hospitals have instituted procedures which include checklists orrequiring multiple counts to be performed to track the use and return ofobjects during surgery. Such a manual approach is inefficient, requiringthe time of highly trained personnel, and is prone to error.

Another approach employs transponders and a wireless interrogation anddetection system. Such an approach employs wireless transponders whichare attached to various objects used during surgery. The interrogationand detection system includes a transmitter that emits pulsed widebandwireless signals (e.g., radio or microwave frequency) and a detector fordetecting wireless signals returned by the transponders in response tothe emitted pulsed wideband signals. Such an automated system mayadvantageously increase accuracy while reducing the amount of timerequired of highly trained and highly compensated personnel. Examples ofsuch an approach are discussed in U.S. Pat. No. 6,026,818, issued Feb.22, 2000, and U.S. Patent Publication No. U.S. 2004/0250819, publishedDec. 16, 2004.

Commercial implementation of such an automated system requires that theoverall system be cost competitive and highly accurate. In particular,false negatives must be avoided to ensure that objects are notmistakenly left in the patient. Some facilities may wish to install asingle interrogation and detection system in each surgery theater, whileother facilities may move an interrogation and detection system betweenmultiple surgical theaters. In either case, the overall system willrequire a large number of transponders, since at least one transponderis carried, attached or otherwise coupled to each object which may orwill be used in surgery. Consequently, the transponders must beinexpensive. However, inexpensive transponders typically have arelatively large variation in the frequency of signals they emit, makingit difficult to accurately detect the signals returned by thetransponders. This may be particularly difficult in some environmentswhich are noisy with respect to the particular resonant frequencies ofthe transponders. Consequently, a new approach to detection of thepresence and absence of transponder that facilitates the use ofinexpensive transponders is highly desirable.

BRIEF SUMMARY

A transponder detection device to detect surgical objects in a workarea, the surgical objects marked by respective resonant tag elementsthat produce return signals in response to energization may besummarized as including: a hand-held probe which includes: asubstantially spherically shaped coil form that includes three coilsupport channels, each of the three coil support channels defines anouter coil support surface; a first antenna element which includes afirst electrical wire wound around the outer coil support surface of afirst one of the three coil support channels, the first antenna elementarranged to transmit and receive signals generally in a first coordinatedirection; a second antenna element which includes a second electricalwire wound around the outer coil support surface of a second one of thethree coil support channels over the first electrical wire, the secondantenna element arranged to transmit and receive signals generally in asecond coordinate direction orthogonal to the first coordinatedirection; a third antenna element which includes a third electricalwire wound around the outer coil support surface of a third one of thethree coil support channels over the first electrical wire and thesecond electrical wire, the third antenna element arranged to transmitand receive signals generally in a third coordinate direction orthogonalto the first coordinate direction and the second coordinate direction; aprocessor operatively coupled to the first antenna element, the secondantenna element, and the third antenna element; and a nontransitoryprocessor-readable medium communicatively coupled to the processor andthat stores at least one of instructions or data executable by theprocessor, which cause the processor to: control each of the firstantenna element, the second antenna element and the third antennaelement to emit wideband interrogation signals; receive any of thereturn signals from any of the resonant tag elements; and determine froma receipt of any of the return signals whether any of the resonant tagelements are present in the work area.

Each of the three coil support channels may be shaped as a sphericalzone of a virtual sphere. Each of the three coil support channels may beshaped as a spherical zone of a virtual sphere centered on a greatcircle of the virtual sphere. The three coil support channels may beshaped as a spherical zones of the substantially spherically shaped coilform centered on respective orthogonal great circles of the coil form.The hand-held probe may further include: a housing that includes acavity sized and shaped to receive the coil form therein. Thetransponder detection device may further include: a light source coupledto the housing that provides a visual indication of at least a status ofthe transponder detection device. The cavity of the housing may bedefined by a substantially spherical body portion, and the housing mayfurther include a handle portion coupled to the body portion. The handleportion may include a handle portion cavity, and the hand-held probe mayfurther include: a circuit board disposed within the handle portioncavity and electrically coupled to the first antenna element, the secondantenna element and the third antenna element. The transponder detectiondevice may further include: a cable coupled to the handle portion andelectrically coupled to the circuit board to couple the first antennaelement, the second antenna element and the third antenna element to thefirst electronic circuit and the second electronic circuit. Theprocessor: may control each of the first antenna element, the secondantenna element and the third antenna element to emit widebandinterrogation signals in time-wise succession during a transmit portionof respective transmit and receive cycles, and may control each of thefirst antenna element, the second antenna element and the third antennaelement to not emit wideband interrogation signals during a receiveportion of respective transmit and receive cycles. The processor mayreceive any of the return signals from any of the resonant tag elementsduring the receive portion of respective transmit and receive cycles.The processor: may filter the any received return signals from noise todetermine whether any of the resonant tag elements are present in thework area. The processor may further: receive a selection of at leastone of a dynamic scan mode and a static scan mode; in response toreceiving a selection of the static scan mode, control each of the firstantenna element, the second antenna element and the third antennaelement to emit wideband interrogation signals according to a staticinstrument scan cycle having a static instrument scan cycle duration;and in response to receiving a selection of the dynamic scan mode,control each of the first antenna element, the second antenna elementand the third antenna element to emit wideband interrogation signalsaccording to a dynamic instrument scan cycle having a dynamic instrumentscan cycle duration that is less than the static instrument scan cycleduration. In response to receiving a selection of the static scan mode,the processor may control each of the first antenna element, the secondantenna element and the third antenna element to emit widebandinterrogation signals centered on a first frequency, and may furthercontrol each of the first antenna element, the second antenna elementand the third antenna element to emit wideband interrogation signalscentered on a second frequency, the second frequency different from thefirst frequency. The static instrument scan cycle duration may be lessthan fifteen (15) seconds and the dynamic instrument scan cycle durationmay be less than five (5) seconds. The processor may further: determinefrom a receipt of any of the return signals whether any of the resonanttag elements are present in the work area based at least in part on afrequency of the return signals received being within a definedfrequency range. The defined frequency range may include the frequencyrange of about 137 kHz to about 160 kHz. The processor may further:determine whether any of the resonant tag elements are present in thework area based at least in part on a Q value of the return signalsreceived. The processor may further: determine whether any of theresonant tag elements are present in the work area based at least inpart on a Q value of the return signals received being at least equal toa threshold Q value. The threshold Q value may be 35. The process mayfurther: determine whether any of the resonant tag elements are presentin the work area based at least in part on a signal detection threshold.The processor may further: receive electromagnetic signals during anoise detection portion; determine a noise value indicative of a noiselevel that corresponds to a number of measurements of theelectromagnetic signals received during the noise detection portion;adjust a signal detection threshold based at least in part on thedetermined noise value; and determine whether any of the resonant tagelements are present in the work area based at least in part on a numberof measurements of the return signals received and the adjusted signaldetection threshold. The processor may further: compare a maximum valueof a plurality of matched filter outputs with the adjusted signaldetection threshold. The processor may further: adjust the signaldetection threshold to be approximately twice the determined noisevalue. The processor may further: determine if an output of at least onematched filter during the noise detection portion exceeds a noise faultthreshold indicative of a noise fault. The wideband interrogationsignals may be centered in at least one of a 136 kHz band, a 139 kHzband, a 142 kHz band, a 145 kHz band, a 148 kHz band, a 151 kHz band ora 154 kHz band.

A method to detect surgical objects in a work area, the surgical objectsmarked by respective resonant tag elements that produce return signalsin response to energization may be summarized as including: providing atransponder detection device that includes a hand-held probe thatincludes a substantially spherically shaped coil form that includesthree coil support channels, each of the three coil support channelsdefines an outer coil support surface, a first antenna element whichincludes a first electrical wire wound around the outer coil supportsurface of a first one of the three coil support channels, the firstantenna element arranged to transmit and receive signals generally in afirst coordinate direction, a second antenna element which includes asecond electrical wire wound around the outer coil support surface of asecond one of the three coil support channels over the first electricalwire, the second antenna element arranged to transmit and receivesignals generally in a second coordinate direction orthogonal to thefirst coordinate direction, and a third antenna element which includes athird electrical wire wound around the outer coil support surface of athird one of the three coil support channels over the first electricalwire and the second electrical wire, the third antenna element arrangedto transmit and receive signals generally in a third coordinatedirection orthogonal to the first coordinate direction and the secondcoordinate direction; emitting wideband interrogation signals via thefirst antenna element, the second antenna element and the third antennaelement; receiving any of the return signals from any of the resonanttag elements via at least one of the first antenna element, the secondantenna element and the third antenna element; and determining from areceipt of any of the return signals whether any of the resonant tagelements are present in the work area.

Emitting wideband interrogation signals via the first antenna element,the second antenna element and the third antenna element may include,for each of the first antenna element, the second antenna element andthe third antenna element, emitting a first wideband interrogationsignal centered at a first frequency and emitting a second widebandinterrogation signal centered at a second frequency, the secondfrequency different from the first frequency. The method may furtherinclude: controlling each of the first antenna element, the secondantenna element and the third antenna element to emit widebandinterrogation signals in time-wise succession during a transmit portionof respective transmit and receive cycles and controlling each of thefirst antenna element, the second antenna element and the third antennaelement to not emit wideband interrogation signals during a receiveportion of respective transmit and receive cycles. The method mayfurther include: filtering the any received return signals from noise todetermine whether any of the resonant tag elements are present in thework area. The method may further include: controlling each of the firstantenna element, the second antenna element and the third antennaelement to emit wideband interrogation signals according to a staticinstrument scan cycle having a static instrument scan cycle duration;and controlling each of the first antenna element, the second antennaelement and the third antenna element to emit wideband interrogationsignals according to a dynamic instrument scan cycle having a dynamicinstrument scan cycle duration that is less than the static instrumentscan cycle duration. The transponder detection device may include a userinterface, the method further including: receiving a selection of atleast one of the dynamic instrument scan cycle and the static instrumentscan cycle via the user interface. The method may further include: inresponse to receiving a selection of the static instrument scan cycle,controlling each of the first antenna element, the second antennaelement and the third antenna element to emit wideband interrogationsignals centered on a first frequency; and controlling each of the firstantenna element, the second antenna element and the third antennaelement to emit wideband interrogation signals centered on a secondfrequency, the second frequency different from the first frequency. Thestatic instrument scan cycle duration may be less than fifteen (15)seconds and the dynamic instrument scan cycle duration may be less thanfive (5) seconds. The method may further include: determining from areceipt of any of the return signals whether any of the resonant tagelements are present in the work area based at least in part on afrequency of the return signals received being within a definedfrequency range. The method may further include: determining whether anyof the resonant tag elements are present in the work area based at leastin part on a Q value of the return signals received. The method mayfurther include: determining whether any of the resonant tag elementsare present in the work area based at least in part on a Q value of thereturn signals received being at least equal to a threshold Q value. Themethod may further include: determining whether any of the resonant tagelements are present in the work area based at least in part on a signaldetection threshold. The method may further include: receivingelectromagnetic signals during a noise detection portion; determining anoise value indicative of a noise level that corresponds to a number ofmeasurements of the electromagnetic signals received during the noisedetection portion; adjusting a signal detection threshold based at leastin part on the determined noise value; and determining whether any ofthe resonant tag elements are present in the work area based at least inpart on a number of measurements of the return signals received and theadjusted signal detection threshold. The method may further include:comparing a maximum value of a plurality of matched filter outputs withthe adjusted signal detection threshold. The method may further include:adjusting the signal detection threshold to be approximately twice thedetermined noise value. The method may further include: determining ifan output of at least one matched filter during the noise detectionportion exceeds a noise fault threshold indicative of a noise fault.

A method of operating a transponder detection device that includes aprocessor, at least one nontransitory processor-readable mediumcommunicatively coupled to the processor and which stores at least oneof instructions or data executable by the at least one processor, and ahand-held probe that includes a first antenna element, a second antennaelement, and a third antenna element, the first, second, and thirdantenna elements arranged orthogonal to each other, the first, second,and third antenna elements operatively coupled to the processor may besummarized as including: receiving a selection of at least one of astatic scan mode and a dynamic scan mode; in response to receiving aselection of the static scan mode, controlling each of the first,second, and third antenna elements to emit wideband interrogationsignals according to a static instrument scan cycle having a staticinstrument scan cycle duration; and in response to receiving a selectionof the static scan mode, controlling each of the first, second, andthird antenna elements to emit wideband interrogation signals accordingto a dynamic instrument scan cycle having a dynamic instrument scancycle duration that is less than the static instrument scan cycleduration.

A transponder detection device may be summarized as including: a coilform that includes three coil support channels, each of the coil supportchannels curved about a respective primary axis and curved about arespective secondary axis orthogonal to the respective primary axis, theprimary axes orthogonal to one another.

The transponder detection device may further include: a first antennaelement which includes a first electrical wire wound around a first oneof the three coil support channels; a second antenna element whichincludes a second electrical wire wound around a second one of the threecoil support channels over the first electrical wire; and a thirdantenna element which includes a third electrical wire wound around athird one of the three coil support channels over the first electricalwire and the second electrical wire. The transponder detection devicemay further include: a processor operatively coupled to the firstantenna element, the second antenna element, and the third antennaelement; and a nontransitory processor-readable medium communicativelycoupled to the processor and that stores at least one of instructions ordata executable by the processor, which cause the processor to: controleach of the first antenna element, the second antenna element and thethird antenna element to emit wideband interrogation signals; receivereturn signals from one or more resonant tag elements; and determinefrom a receipt of any of the return signals whether any of the resonanttag elements are present in the work area. Curvatures of the three coilsupport channels about the respective primary axes may be equal to oneanother and equal to curvatures of the coil support channels about therespective secondary axes.

A transponder detection device may be summarized as including: a coilform including: a first coil support channel curved about a primary axisdefined by a first axis and curved about a secondary axis defined by asecond axis orthogonal to the first axis; a second coil support channelcurved about a primary axis defined by third axis and curved about asecondary axis defined by the first axis, the third axis orthogonal tothe first axis and the second axis; and a third coil support channelcurved about a primary axis defined by the second axis and curved abouta secondary axis defined by the first axis.

Curvatures of the first, second, and third coil support channels aboutthe respective primary axes may be equal to one another and equal tocurvatures of the first, second, and third coil support channels aboutthe respective secondary axes. The transponder detection device mayfurther include: a first antenna element including a first electricalwire wound around the first coil support channel; a second antennaelement including a second electrical wire wound around the second coilsupport channel over the first electrical wire; and a third antennaelement including a third electrical wire wound around the third coilsupport channel over the first electrical wire and the second electricalwire. The transponder detection device may further include: a processoroperatively coupled to the first antenna element, the second antennaelement, and the third antenna element; and a nontransitoryprocessor-readable medium communicatively coupled to the processor andthat stores at least one of instructions or data executable by theprocessor, which cause the processor to: control each of the firstantenna element, the second antenna element and the third antennaelement to emit wideband interrogation signals; receive return signalsfrom one or more resonant tag elements; and determine from a receipt ofany of the return signals whether any of the resonant tag elements arepresent in the work area.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn, are notintended to convey any information regarding the actual shape of theparticular elements, and have been solely selected for ease ofrecognition in the drawings.

FIG. 1 is a schematic diagram showing a surgical environmentillustrating a medical provider using an interrogation and detectionsystem to detect an object tagged with a transponder in a patient,according to one illustrated embodiment.

FIG. 2A is a schematic diagram of a transponder, according to oneillustrated embodiment.

FIG. 2B is a schematic diagram of a transponder, according to anotherillustrated embodiment.

FIG. 2C is a schematic diagram of a transponder, according to a furtherillustrated embodiment.

FIG. 2D is a side elevational view of a transponder, according to yet afurther illustrated embodiment.

FIG. 2E is an end view of the transponder of FIG. 2D.

FIG. 2F is a cross-sectional view of the transponder of FIG. 2D, takenalong section line 2F.

FIG. 2G is an isometric view of a ferrite core of the transponder ofFIG. 2D.

FIG. 3A is an isometric view of a probe of the interrogation anddetection system, according to one illustrated embodiment.

FIG. 3B is an isometric view of a coil form and three mutuallyorthogonal coils of the probe of FIG. 3A.

FIG. 4 is an isometric view of a controller of the interrogation anddetection system, according to one illustrated embodiment.

FIG. 5 is a schematic diagram of a control system of the interrogationand detection system, according to one illustrated embodiment.

FIG. 6 is a schematic diagram of a software configuration of theinterrogation and detection system, according to one illustratedembodiment.

FIG. 7 is a flow diagram of a method of operating an interrogation andcontrol system, according to one illustrated embodiment.

FIG. 8 is a flow diagram showing a method of operating an interrogationand detection system according to one illustrated embodiment, includingreceiving electromagnetic signals, for example unmodulatedelectromagnetic signals, determining a noise value, adjusting signaldetection threshold, emitting interrogations signals, receivingelectromagnetic signals, and determining a presence or absence of atransponder based at least in part on the adjusted signal detectionthreshold.

FIG. 9 is a graph showing noise and signal levels when the signal issampled using subsample scan cycles, according to one illustratedembodiment.

FIG. 10 is a timing diagram illustrating interrogation cycle timing,according to one illustrated embodiment.

FIG. 11A is a timing diagram illustrating a scan cycle, according to oneillustrated embodiment.

FIG. 11B is a timing diagram illustrating a coil scan cycle, accordingto one illustrated embodiment.

FIG. 11C is a timing diagram illustrating a frequency specific samplecycle, according to one illustrated embodiment.

FIG. 11D is a timing diagram illustrating a subsample scan cycle,according to one illustrated embodiment.

FIG. 12 is a timing diagram illustrating timing for obtaining subsamplesutilizing subsample scan cycles, according to one illustratedembodiment.

FIG. 13 is a flow diagram showing a process for a scanning method,according to one illustrated embodiment.

FIG. 14 is a flow diagram showing a process for a scanning method usedwith multiple coils, according to one illustrated embodiment.

FIG. 15 is a flow diagram showing a process for implementing a dynamicinstrument scan cycle and a static instrument scan cycle, according toone illustrated embodiment.

FIG. 16 is a flow diagram showing a method of determining the presenceor absence of a transponder by evaluating one or more subsamples,according to one illustrated embodiment.

FIG. 17 is an isometric, partially exploded view of the probe of theinterrogation and detection system also shown in FIG. 3A.

FIG. 18 is a partially disassembled view of the probe of theinterrogation and detection system, illustrating a coil form, orthogonalcoils, and a circuit board.

FIG. 19A is an isometric view of the coil form of the probe of theinterrogation and detection system.

FIG. 19B is an elevational view of the coil form shown in FIG. 19A.

FIG. 20 is an isometric view of an inner surface of a right housing ofthe probe of the interrogation and detection system, illustrating analignment rib.

FIG. 21 is a sectional view of a coil of the probe, and a sectional viewof a transponder disposed proximate to the coil.

FIG. 22A is a front elevational view of a mobile transport system forthe probe of the interrogation and detection system, according to oneillustrated embodiment.

FIG. 22B is a right side elevational view of the mobile transport systemshown in FIG. 22A.

FIG. 23A is an elevational view of the coil form illustrating a radiusof a length of an outer surface of a coil form channel.

FIG. 23B is an elevational view of the coil form illustrating a radiusof a width of an outer surface of a coil form channel.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with transmitters,receivers, or transceivers have not been shown or described in detail toavoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments.

FIG. 1 shows a surgical environment 100 in which a medical provider 102operates an interrogation and detection system 104 to ascertain thepresence or absence of objects 106 in, or on, a patient 108. Theinterrogation and detection system 104 may include a controller 110, andone or more antennas 306 (see FIG. 3B) coupled to the controller 110 byone or more communication paths, for example coaxial cable 114. Theantennas may be housed within a hand-held probe 112 that may include oneor more antenna coils, for example. While designated as a probe, theblunt instrument is not necessarily intended to explore a wound or toeven enter a patient's body. In many applications the hand-held probewill remain on the exterior outside of the patient's body. In someapplications, for example labor and delivery (L&D), the patient may nothave a wound.

The object 106 may take a variety of forms, for example instruments,accessories and/or disposable objects useful in performing surgicalprocedures. For instance, the object 106 may take the form of scalpels,scissors, forceps, hemostats, and/or clamps. Also for example, theobjects 106 may take the form of surgical sponges, gauze and/or padding.The object 106 is tagged, carrying, attached or otherwise coupled to atransponder 116. Embodiments of the interrogation and detection system104 disclosed herein are particularly suited to operate withtransponders 116 which are not accurately tuned to a chosen or selectedresonant frequency. Consequently, the transponders 116 do not requirehigh manufacturing tolerances or expensive materials, and thus may beinexpensive to manufacture.

In use, the medical provider 102 may position the probe 112 proximatethe patient 108 in a fixed or static position to detect the presence orabsence of the transponder 116 and hence an object 106. The medicalprovider 102 may in some embodiments dynamically move the probe 112along and/or across the body of the patient 108 or may move the probenear other areas, such as a near a trash can or drape bag in a surgeryroom. In some embodiments, the probe 112 may be sized to fit at leastpartially in a body cavity 118 of the patient 108.

FIG. 2A shows a transponder 116 a according to one illustratedembodiment.

The transponder 116 a includes a miniature ferrite rod 230 with aconductive coil 232 wrapped about an exterior surface thereof to form aninductor (L), and a capacitor (C) 234 coupled to the conductive coil 232to form a series LC circuit. The conductive coil 232 may, for example,take the form of a spiral wound conductive wire with an electricallyinsulative sheath or sleeve. The transponder 116 a may include anencapsulant 236 that encapsulates the ferrite rod 230, conductive coil232, and capacitor 234. The encapsulant 236 may be a bio-inert plasticthat protects the ferrite rod 230, conductive coil 232 and/or capacitor234 from pressure and/or from fluids, for example bodily fluids.

In some embodiments, the ferrite rod 230 may include a passage 238 sizedto receive a physical coupler, for example a bonding tie or string 240.The bonding tie or string 240 may take the form of an elastomeric x-rayopaque flexible elongated member, that may be used to attach thetransponder 116 a to various types of objects 106, for example surgicalsponges. The transponder 116 a may have a length of about 8 millimetersand a diameter of about 2 millimeters. Employing such small dimensionsensures that the transponder 116 a does not impede deformation ofobjects 106 such as sponges. The transponder 116 a may include anoptional diode (not shown), to protect against over-voltage occurrencescaused by other electronic instruments.

FIG. 2B shows a transponder 116 b, according to another illustratedembodiment.

The transponder 116 b includes a single loop of conductive material 242,for example a loop of conductive wire forming an inductor (L), coupledin series to a capacitor 244 (C) to form an LC series circuit. The loopof conductive material 242 and capacitor 244 may be encapsulated in anelastomeric coating or sleeve 246. The dimensions of the transponder 116b may be similar to the dimensions of the transponder 116 a. In someembodiments, the dimensions of the transponder 116 b are greater thanthe dimensions of the transponder 116 a. The transponder 116 b is highlyflexible, and thus may provide its own thread-like or string-likeattachment to various types of objects 106.

FIG. 2C shows a transponder 116 c according to a further embodiment.

The transponder 116 c includes a dumbbell-shaped ferrite rod 248 havingbroad end portions 248 a, 248 b, and a narrow intermediate portion 248 cwhich is wrapped by a conductive coil 250. The broad end portions 248 a,248 b contain the conductive coils 250. Such a design may providestronger and/or more reliable signal emission than transponders 116 a,116 b fashioned with cylindrical ferrite rods. The transponder 116 c mayoptionally include an encapsulant 252. Further details regarding thetransponder 116 c may be found in U.S. Provisional Patent ApplicationNo. 60/811,376 filed Jun. 6, 2006. In some embodiments, the transponder116 c may be formed as a fusiform-shaped object, with truncated ends.The fusiform shape may be advantageous over cylindrical shapedtransponders 116 a, 116 b in reducing the likelihood of close parallelalignment of the transponders 116 a, 116 b, which may producetransponder-to-transponder interaction and interference.

FIGS. 2D-2G show a transponder 116 d according to yet a furtherembodiment.

The transponder 116 d includes a ferrite core 253, inductor (L) 254, andcapacitor (C) 255 electrically coupled to the inductor 254 to form an LCseries circuit. The transponder 116 d also includes a capsule 256 with acavity 257 open at one end to receive the ferrite core 253, inductor 254and capacitor 255, as well as a lid 258 to close the open end of thecapsule 256.

The ferrite core 253 may, for example, take the form of a soft ferritedrum, and may, for example, be formed of Nickel Zinc. Suitable ferritecores 253 may be commercially available from TAK FERRITE as part no. L8ADR3X9 B=1.8 F=6 or from HUAH YOW under part no. 10R030090-77S. The drummay have a pair of larger diameter end portions 253 a, 253 b, with asmaller diameter intermediate portion 253 c therebetween.

The inductor 254 may take the form of magnet wire wrapped around theintermediate portion 253 c of the ferrite core 253. The magnet wire may,for example, have a dimension of approximately 41 American Wire Gauge(AWG), although some embodiments may employ wires or conductors oflarger or small gauges. Suitable inductors 254 may be commerciallyavailable from ELEKTISOLA under part no. PN-155 or from ROSEN under partno. 2UEW-F. The inductor may, for example, include approximately 432turns, over approximately 6.5 layers, although some embodiments mayinclude a greater or lesser number of turns and/or layers. Thetransponder 116 d may include tape and/or epoxy enveloping the inductor254. Suitable tape may be commercially available from 3M under part nos.1298, 1350-1 or PLEO 1P801, while suitable epoxy may be commerciallyavailable from LOCKTITE under part no. 3211.

The capacitor 255 may, for example, take the form of a ceramiccapacitor. The capacitor 255 may, for example, have a capacitance of 470PF, 100V, with a Quality factor of Q>2200 @ 1 MHz. Suitable capacitors255 may be commercially available from SANJV DIELECTRIC under part no.0805NPO471J101 or from FENG HUA under part no. 0805CG471J101NT.

The capsule 256 and lid 258 may, for example, be formed of apolypropylene. Suitable capsules 256 and lids 258 may be commerciallyavailable from WEITHE ELECTRON (HK) COMPANY, under part specificationCASE 4.3×12.6. The combination of the capsule 256 and lid 258 may, forexample, have a length of approximately 12.8 mm and a diameter of 4.4mm. Circuit bonds may, for example, employ UNITED RESINS CORP. part no.63001500 CIRCUIT BOND LV, while solder may take the form of a lead free96.5% Ag/3% Sn/0.5 Cu solder.

The transponders 116 may be attached to hemostats, scissors, certainforms of forceps, and the like. In some embodiments, the transponders116 may be coupled to the object 106 by way of a clamp or holder. Insome embodiments, the transponders 116 may be retained within a cavityof the holder. In some embodiments, the holder may be fashioned of adurable deformable material, such as surgical grade polymer, which maybe deformed to clamp securely onto the finger or thumbhole of aninstrument. In other embodiments, the transponders 116 may be attachedto objects 106 by way of pouches fashioned of sheet material (e.g.,surgical fabric) surrounding the transponder 116. The transponder 116 isretained within the pouch, and in some embodiments the pouch may be sewnor otherwise sealed. Sealing may be done with adhesive, hot glue,clamping, grommeting, or the like.

FIGS. 3A-B, 17, 18, 19A-B, 20, 21, 22A and 22B show various views of theprobe 112 also illustrated in FIG. 1, according to one illustratedembodiment.

As shown in FIG. 3A, the probe 112 may include a first body portionstructure 302 a and a second body portion structure 302 b that mates tothe first body portion structure 302 a to form a generally sphericalbody portion 302. The first body portion structure 302 a and the secondbody portion structure 302 b may be fixedly coupled together duringmanufacture by any suitable process (e.g., RF welding, friction fit,snap fit, tabs and lips, pins and holes, detents, etc.). The probe 112may include a handle portion 304 extending from the spherical bodyportion 302. The handle portion 304 may be sized and dimensioned to begripped by the hand of a medical provider 102 (FIG. 1). In someembodiments, the handle portion 304 may include an overmolded grippingsurface. The overmolded gripping surface may be a material that providesa relatively high degree of tact and/or may be textured to facilitatenon-slip gripping. In some embodiments, the handle portion 304 may beshaped similar to that of a computer mouse, which is ergonomicallydesirable for the medical provider 102.

The body portion 302 may define a cavity 316 (FIG. 17) therein sized anddimensioned to receive an antenna 306 (FIG. 3B). The antenna 306 may,for example, take the form of air-coil formed of coils of conductivematerial, for example, electrical wire. The antenna 306 acts as aninductor that facilitates magnetic inductive coupling with one or morecoils of a transponder 116.

As shown in FIG. 3B, the antenna 306 may include three antenna coils: anradially inner coil 306 a, a radially middle coil 306 b, and a radiallyouter coil 306 c mutually orthogonal to each other. In the illustratedembodiment, the antenna coils 306 a, 306 b, and 306 c are wound aroundouter surfaces 318 a, 318 b, 318 c, respectively (FIG. 19A), ofrespective coil form channels 320 a, 320 b, and 320 c of a coil form orbobbin 308. Electrical wires or ends 310 a, 310 b, and 310 c (FIG. 3B)of the respective coils 306 a, 306 b, and 306 c may be electricallycoupled to the controller 110 via the cable 114 (FIG. 1). In someembodiments the coil form 308 may be a flexible printed circuit board(e.g., relatively few laminations of FR4). The coil form 308 may includestrain relief structures or features such as notches, or cutoutslaterally across the width of the printed circuit board and/or extendinginto the surface or along the edges of the printed circuit board.

FIG. 17 illustrates an isometric, partially exploded view of the probe112 also shown in FIG. 1. As shown, the body portion 302 and handleportion 304 are formed from three components, a left housing 322 a, aright housing 322 b, and a top housing 324, that are coupled togetherduring a manufacturing process. A printed circuit board 326 may becoupled to the top housing 324 via one or more fasteners (e.g., screws328).

As shown in FIGS. 17 and 18, the electrical wires 310 a, 310 b, and 310c, of the respective coils 306 a, 306 b, and 306 c may be coupled to theprinted circuit board 326, which may in turn be coupled to a wire 330(FIG. 18) of a coupling member 312, which may be positioned in thecavity in the handle portion 304 to provide a connector tocommunicatively couple to an end of the coaxial cable 114 to the antennacoils 306 a, 306 b, and 306 c. The coupling member 312 may take the formof a standard coaxial connector. Some embodiments may employ other typesof communications pathways between the controller 110 and the antenna306, and thus may employ other types of coupling members or connectors.

In some embodiments, the probe 112 may include one or more userinterface devices, for example one or more visual indicators 314 (FIG.3A) to provide visual indications to the medical provider 102. Such may,for example, take the form of one or more light emitting diodes 332(FIG. 17), which may provide one or more different colors. Such userinterface devices may additionally or alternatively include a speaker orother transducer (e.g., piezoelectric transducer, electric motor),operable to provide a sound or other sensory indication, for example atactile sensation (e.g., vibration). Such user interface devices may beoperable to provide sensory feedback to the medical provider 102indicative of an operating condition of the interrogation and detectionsystem 104. For example, such may indicate when the interrogation anddetection system 104 is operating, when the presence of a transponder116 has been identified, and/or when an error has occurred. Locatinguser interface devices on the probe 112 may be advantageous since themedical provider 102 will typically focus their attention on the probe112 while scanning the patient 108.

In the illustrated embodiment, the printed circuit board includes thelight emitting diode 332 (FIG. 17) disposed thereon. A light pipe 334may be positioned within an aperture 336 of the top housing 324. Thelight pipe 334 is light transmissive such that light from the lightemitting diode 332 may pass through the light pipe where it is visibleby a user. The light emitting diode 332 may be used to provide a visualindication to a user of the probe 112, such as status information oroperational information.

As shown in FIGS. 3B, 19A and 19B, the generally spherical coil form 308includes the three mutually orthogonal coil form channels 320 a, 320 b,and 320 c each having a respective outer surface 318 a, 318 b, and 318 cfor supporting a respective one of the coils 306 a, 306 b, and 306 c. Asshown in FIG. 19A, the first coil form channel 320 a is oriented in anXY plane, the second coil form channel 320 b is oriented in an XZ plane,and the third coil form channel 320 c is oriented in a YZ plane. Thethree coil form channels 320 a, 320 b, and 320 c may intersect eachother or may be nested. Each of the three coil form channels 320 a, 320b, and 320 c defines its respective outer coil support surface 318 a,318 b, and 318 c. Each outer coil support surface 318 a, 318 b, 318 c issubstantially cylindrically shaped with a curved surface. Morespecifically, in the illustrated embodiment each outer coil supportsurface 318 a, 318 b, and 318 c is shaped as a spherical zone of avirtual sphere, the spherical zone having a width W (FIG. 19B) and beingcentered on a great circle of the virtual sphere. As used herein, agreat circle of a sphere is the intersection of the sphere and a planewhich passes through the center point of the sphere. As used herein, aspherical zone is the surface of a spherical segment, which is a soliddefined by cutting a sphere with a pair of parallel planes. In thiscase, the parallel planes are also parallel to a great circle of thevirtual sphere and spaced apart on each side of the great circle by anequal distance (i.e., W/2), such that the spherical segment is centeredon the great circle.

As shown in FIGS. 23A and 23B, each of the outer coil support surfaceshave a circumference or length L that is defined by a body of revolutionabout a respective primary axis and a width W that is curved about arespective secondary axis orthogonal to the primary axes. Specifically,the length L of the outer coil support surface 318 a is defined by arevolution about the Z axis (FIG. 23A) and the width W is curved aboutthe X axis (FIG. 23B). The length L of the outer coil support surface318 b is defined by a revolution about the Y axis and the width W iscurved about the Z axis. The length L of the outer coil support surface318 c is defined by a revolution about the X axis and the width W iscurved about the Z axis.

The curvatures of the length L and the width W of each of the outer coilsupport surfaces 318 a-c are equal to each other. For example, thelength L of the outer coil surface 318 a at its center may be defined bya circle in the XY plane having a curvature radius R_(L-318a) (FIG.23A). The width W of the outer coil surface 318 a has a radius ofcurvature of R_(W-318a) (FIG. 23B), which is equal to the radiusR_(L-318a) of the length L.

As shown in FIGS. 19A and 19B, eight apertures 340 shaped as sphericaltriangles may be defined by the intersection of the coil form channels320 a, 320 b, and 320 c. The size of the eight apertures 340 isdependent on the width W of the coil form channels 320 a, 320 b, and 320c. That is, the wider the width W of coil form channels 320 a, 320 b,and 320 c, the smaller the eight apertures 340. In some embodiments, theapertures 340 are not present and the coil form 308, such that the coilform is substantially shaped as a sphere without apertures therein. Insome embodiments, the interior of the coil form 308 may be hollow,whereas in other embodiments one or more materials may be present withinthe interior of the coil form.

As shown in FIG. 20, an interior surface 342 of the right housing 322 bmay include an alignment rib 344 shaped and sized to be inserted intoone of the spherical triangle-shaped apertures 340 of the coil form 308.Although not shown in the figures, the left housing 322 a may besubstantially the same as the right housing 322 b and may also includean alignment rib on an interior surface thereof. The alignment ribs onthe interior surfaces of the housings 322 a and 322 b align the coilform 308 relative to the housing during manufacturing and fix theposition of the coil form with respect to the assembled housing.

As shown in FIG. 3B, the first coil 306 a is wound around the outer coilsupport surface 318 a of the first coil support channel 320 a to form afirst antenna element arranged in the XY plane so as to transmit andreceive signals primarily in the orthogonal z-axis direction. The secondcoil 306 b is wound around the outer coil support surface 318 b of thesecond coil support channel 320 b over the first coil 306 a to form asecond antenna element in the XZ plane so as to transmit and receivesignals primarily in the orthogonal y-axis direction. The third coil 306c is wound around the outer coil support surface 318 c of the third coilsupport channel 320 c over the first coil 306 a and over the second coil306 b to form a third antenna element in the YZ plane so as to transmitand receive signals primarily in the orthogonal x-axis direction.

By providing three mutually orthogonal coils 306 a-c within thespherical body portion 302 of the probe 112, the likelihood of detectinga transponder at a given distance is improved. This is illustrated withreference to FIG. 21, which shows a sectional view of the second coil306 b disposed in the XZ plane and configured to transmit and receivesignals primarily in the orthogonal y-axis direction, and a sectionalview of the transponder 116 d positioned proximate to the second coil.The efficiency of the coupling between the second coil 306 b and theinductor or coil 254 of the transponder 116 d is proportional to thepresentation angle of the two coils relative to each other. Maximumcoupling occurs when the two coils are in a parallel relationship (i.e.,an angle θ=0 degrees). This condition results in maximum induced voltagein the transponder coil 254 and a maximum read range. As the transponder116 d is rotated with respect to the second coil 306 b, the magneticcoupling is reduced by the cosine of the angle of rotation (i.e., acosine θ variation). Thus, when the two coils 306 and 254 are in aperpendicular relationship (i.e., angle θ=90 degrees), magnetic couplingis minimized (e.g., a “dead zone”). Under conditions of minimumcoupling, it is less likely that the second coil 306 b will be able todetect the transponder 116 d.

By utilizing three mutually orthogonal coils 306 a-c as opposed to asingle planar coil, it is possible to ensure that the angle θ ofrotation of the transponder coil 254 will always be less than 45 degreeswith respect to at least one of the orthogonal coils 306 a-c. At anangle θ of rotation of 45 degrees (i.e., “worst case” orientation), themagnetic coupling is approximately 71% of the maximum or optimummagnetic coupling (i.e., cosine 45 degrees=0.707). Thus, the use ofthree orthogonal coils 306 a-c ensures that the magnetic couplingbetween the transponder coil 254 and at least one of the coils 306 a-cof the probe 112 will always be at least 71% of the maximum couplingorientation. Accordingly, given the same transmit energy, transponders116 may be detected at a greater distance using the three orthogonalcoils 306 a-c as compared to using a single planar coil. Additionally oralternatively, the probe 112 may transmit signals at lower energy levelsto achieve a similar read range as a single planar coil transmitting ata higher energy level.

FIGS. 22A and 22B illustrate front and right side elevational views,respectively, of a mobile transport system 2200 for use with the probe112 and console 110, according to one illustrated embodiment. A mountingplate 2202 is coupled to a top end of a vertical pole 2204. The mountingplate 2202 provides an attachment surface for securing the console 110thereto. A bottom end of the vertical pole 2204 is coupled to a base2206, which in turn is coupled to a plurality of wheels 2208. In someembodiments, the vertical pole 2204 may be expandable or contractible toadjust a height thereof. The mobile transport system 2200 may include abasket 2210 secured to the vertical pole 2204 by one or more brackets2212. The basket 2210 may be used to hold one or more medical supplies,for example. A handle 2214 may be attached to the vertical pole 2204. Inuse, an operator may grasp the handle 2214 and move the mobile transportsystem 2200 by exerting a force on the handle to push or pull the mobiletransport system so that it rolls on the wheels 2208. The vertical pole2204 also includes a probe support member or holster 2216 attachedthereto. The holster 2216 is shaped and sized to support the probe 112therein. The mobile transport system 2200 allows the probe 112 andconsole 110 to be easily moved from one location to another whilemaintaining a small footprint, which can be advantageous in settingswhere space is limited.

FIG. 4 shows the controller 110 according to one illustrated embodiment.The controller 110 includes an input port 420 with an appropriatecoupling member, for example a connector to allow an end of the coaxialcable 114 to be communicatively coupled to the controller 110. As notedabove, some embodiments may employ other communications pathways betweenthe controller 110 and the antenna 306, hence other types of couplingmembers or connectors may be employed. The controller 110 may alsoinclude a power switch (not illustrated in FIG. 4), for example,positioned on a back or rear of the controller 110. The controller 110may further include a power cord (not shown) to couple the controller110 to a suitable power supply. The power supply may, for example takethe form of a standard wall outlet or any other power supply or source.The controller 110 may further include one or more user interfacedevices for providing information to a user. For example, the controller110 may include one or more visual indicators, for instance one or morelight emitting diodes (LEDs) 434 a-f and/or liquid crystal displays.Additionally, or alternatively, the controller 110 may include one ormore speakers 430 or other transducers operable to produce sound ortactile sensations. The controller 110 forms a transmitter and receiver,or transceiver, to transmit interrogation signals and receive responsesto those signals, as well as to receive electromagnetic signals whichmay be indicative of noise.

FIG. 5 shows a control system 500 of the interrogation and detectionsystem 104, according to one illustrated embodiment.

The control system 500 includes a field programmable gate array (FPGA)board 502, analog board 504 and display board 506, communicativelycoupled to one another.

The FPGA board includes an FPGA 508, configuration jumpers 510, RS-232drivers 512, oscillator 514, random access memory (RAM) 516, flashmemory 518, and voltage monitoring (VMON) analog-to-digital converter(ADC) 520. The FPGA 508 may take the form of a Xilinx Spartan3 FPGA,which runs FPGA and application software. As explained below, on powerup, the FPGA reads the configuration information and applicationsoftware program from the flash memory 518.

The configuration jumpers 510 are used to select the applicationsoftware configuration.

The RS-232 drivers 512 are used to allow the application software tocommunicate using serial RS-232 data for factory test and diagnostics.

The oscillator 514 sets the clock frequency for the operation of theFPGA 508. The oscillator 514 may, for example, take the form of 40 MHzoscillator, although other frequencies are possible.

The RAM 516 is connected to the FPGA 508 and is available for use by theapplication software. The application software uses this memory spacefor storage of both the executable program and program data. The RAM 516may, for example, have a capacity of 1 MB.

The flash memory 518 contains both the FPGA configuration data and thebinary application program. On power up the FPGA 508 reads the flashmemory to configure the FPGA 508 and to copy the application programbinary data from the flash memory 518 to the RAM 516.

The voltage monitor ADC 520 is connected to the FPGA 508 and controlledby the application software to monitor a power supply and regulatedvoltage forms in controller electronics.

The analog board 504 includes transmit control circuits 522, capacitorselection circuits 524, probe detection circuit 526, signal ADC 528,audible beeper 430 and self-test signal 532.

The transmit control circuits 522 on the analog board 504 are controlledby signals from the FPGA 508 to generate a transmit waveform.

Optional capacitor selection circuits 524 on the analog board 504 arecontrolled by the signals from the FPGA 508 to tune the drive circuit tomatch an inductance of the antenna 306.

The probe detection circuit 526 detects when a probe 112 is connected tothe controller 110. The output of the probe detection circuit 526 drivesa signal denominated as the LOOP_LEVEL_OUT signal, which is an input tothe FPGA 508.

The signal ADC 528 is used as a receiver to sample the signals receivedat the antenna 306 from the transponders 116 (FIGS. 2A-2C). The signalADC 528 may, for example, operate at a 1 MHz sample rate and may have12-bits of resolution. The FPGA board 502 generates the timing andcontrol signals for the signal ADC 528, which signals are denominated asADC_CTRL, CS1, SCLK, and SD0.

The audible speaker or beeper 430 can be controlled by the FPGA 508 toemit sounds to indicate various states, modes or operating conditions tothe medical provider 102 (FIG. 1).

The FPGA 508 can cause the generation of the self-test signal 532 on theanalog board 504 at the signal ADC 528. Self-testing may be performed atstart up, and/or at other times, for example periodically or in responseto the occurrence of certain conditions or exceptions.

The display board 506 includes user interface elements, for example anumber of light emitting diodes (LEDs) 434. The FPGA board 502 cancontrol the LEDs 434 on the display board 506. The display board 506also includes a user selectable activation switch, denominated as frontpanel button 436. The front panel button 436 is connected to the displayboard 506 which allow the FPGA 508 to monitor when the front panelbutton 436 is activated (e.g., pressed).

FIG. 6 shows a software configuration 600 of the interrogation anddetection system 104, according to one illustrated embodiment.

The software may include application software 602 that is responsiblefor operating the controller 110 (FIGS. 1 and 4). The applicationsoftware 602 controls the timing for generating transmit pulses,processes sampled data to detect transponders 116 (FIGS. 2A-2C), andindicates status to the user with the display LED's 434 (FIG. 5) on thedisplay board 506 and/or via the audible speaker or beeper 130 on theanalog board 504. The application software 602 is stored in the flashmemory 518 (FIG. 5) and transferred into the RAM 516 by a boot loader604.

The boot loader 604 is automatically loaded when the FPGA 508 isconfigured, and starts execution after a processor core 606 is reset.The boot loader 604 is responsible for transferring the applicationsoftware 602 from the flash memory 518 to the external RAM 516.

The processor platform 608 is configured into the FPGA 508 (FIG. 5) onpower up from the configuration information stored in the flash memory518. The processor platform 608 implements a custom microprocessor witha processor core 606, peripherals 610 a-610 n, and custom logic 612.

The processor core 606 may take the form of a soft processor coresupplied by XILINX under the name MICROBLAZE, that implements a 32-bitprocessor including memory cashes and a floating point unit. A soft coreprocessor is one that is implemented by interconnected FPGA logic cellsinstead of by a traditional processor logic. The processor core 606 isconnected to the internal FPGA peripherals 610 a-610 n using a 32-bitprocessor bus 611 called the On-Chip Peripheral Bus. The XILINX suppliedperipherals for the MICROBLAZE processor core 606 include externalmemory interfaces, timers, and general purpose I/O.

The custom logic 612 to create the transmit signals, sample the ADC 128,and accumulate the transponder return signals is designed as aperipheral to the processor core 606. The custom logic 612 is the partof the design of the FPGA 508.

In some embodiments, a detection cycle that employs an approach thatoptimizes signal to noise ratio (SNR) by a receiver portion may beimplemented. Such may, for example, advantageously increase range orincrease sensitivity at a given range. One embodiment is optimized basedon having an overall detection cycle that performs well for transponderswith resonant frequencies from approximately 136 kHz to approximately154 kHz.

The application software 602 (FIG. 6) implements the detection cycleusing transmission or interrogation in a frequency band centered arounda center channel or frequency. The application software 602 sequencesthrough a non-measurement portion (i.e., gap), and two distinctmeasurement portions, denominated as a noise detection portion and ansignal measurement portion, each detection cycle. In at least oneembodiment, the detection cycle may, for example, be approximately 275milliseconds, the gap portion may be approximately 10 milliseconds, thenoise portion approximately 37 milliseconds and the signal measurementportion approximately 228 milliseconds.

During the noise detection portion, which may, for example be a firstmeasurement portion of each detection cycle, ambient or background noiseis measured or sampled, providing a value indicative of a level ofambient or background noise for the particular environment. The noisemeasurements or are taken or captured at a time sufficiently afterexcitement of the transponders 116 by the interrogation signal emittedby the transmitter such that the transponders 116 are substantially notresonating or responding to any previous excitation by interrogationsignals. In particular, a number N of measurements or samples are takenduring the noise detection or first measurement portion.

During the signal measurement portion, which may, for example take theform of the second measurement portion of each detection cycle,responses by transponders 116 are measured or sampled. The responsemeasurements or samples are taken with the transmitter transmitting orat a time sufficiently close to excitement of the transponders 116 bythe interrogation signal emitted by the transmitter such that thetransponders 116 are still substantially resonating or responding to theinterrogation signal. In particular, a number M of measurements orsamples are taken during the interrogation or second measurementportion.

While the signal measurement portion may be one contiguous or continuousportion, in some embodiments the signal measurement portion may take theform of two or more separate portions or intervals. Each of the portionsmay employ the same transmit frequency band, for example centered around145 kHz. Other center channels or frequencies may for example be 136kHz, 139 kHz, 142 kHz, 145 kHz, 148 kHz, 151 kHz and/or 154 kHz, or anyother frequency suitable for exciting the transponder to resonate. Someembodiments may employ frequency hopping, for example transmitting adifferent center channel or frequency for each of a plurality of signalmeasurement portions of each detection cycle. Such is discussed furtherin U.S. provisional patent application Ser. No. 60/892,208, filed Feb.28, 2007 (now U.S. Pat. No. 8,710,957) and U.S. non-provisionalapplication Ser. No. 11/743,104, filed May 1, 2007 (now U.S. Pat. No.7,696,877).

The gap portion may provide time for the response of the transponders116 to the interrogation signal to decay sufficiently to allowmeasurement of noise.

Some embodiments may arrange the gap, the noise detection portion and/orthe signal measurement portion, or parts thereof, in a different order.

In one embodiment, the time to accumulate the noise sample or valueindicative of a noise level may, for example, be approximately 37milliseconds, and the time to accumulate the transponder signalmeasurement approximately 228 milliseconds. Along with a gap ofapproximately 10 milliseconds between the signal and noise portions, thetime for a single detection cycle would be approximately 275milliseconds. As noted above, the transmitter is OFF during the noisemeasurement portion of each detection cycle to allow the receiver tomeasure ambient noise, and the signal detection portion is taken withthe transmitter transmitting a wideband interrogation signal about theparticular center channel or frequency.

The noise samples collected by the receiver may be accumulated and ahighest one or more of multiple samples or measurements over one or moredetection cycles selected or used to prevent unwarranted fluctuations.The response signals from the transponder 116 may be accumulated and/oraveraged or integrated over one detection cycle or over multipledetection cycles.

The number N of noise measurements or samples and/or the number M ofresponse signal measurements or samples may be selected to achieve adesired ratio of N to M, in order to achieve or maintain a desiredsignal to noise ratio. For example, obtaining 200 noise measurements orsamples and 800 response measurements or samples each detection cycleresults in an SNR of approximately 2 (e.g., the square root of the 800divided by 200). While an SNR as low as 1.1:1 may be sufficient in someembodiments, an SNR approaching 2:1 ensures sufficient differentiationto eliminate or reduce the possibility of false positives to anacceptable level for the particular applications envisioned herein. Anyknown hardware and software accumulators, summer, integrators and/orother hardware or software may be suitable.

The accumulated or integrated received signal may be matched filteredwith both in-phase and quadrature reference signals to determine thesignal magnitude. The received receive signal is matched filtered with aplurality of reference signals, for example with the seven referencesignals, for instance as shown in Table 1 below. Some embodiments mayemploy matched filtering before accumulating or integrating the receivedsignal.

TABLE 1 Match Frequency 136 kHz 139 kHz 142 kHz 145 kHz 148 kHz 151 kHz154 kHz

The maximum value for the matched filters (e.g., seven matched filters)with active transmit may be compared with an adjusted detectionthreshold. If the maximum value is greater than the detection threshold,then a response signal from a transponder 116 may be considered ashaving been detected, and appropriate action is taken, such as discussedbelow with reference to FIG. 7. Alternatively or additionally, theinterrogation and detection system may employ a fast Fourier transformapproach in lieu of matched filtering.

The noise filtering processes the measured or sampled noise values foreach detection cycle to determine a stable noise floor value. The outputof the noise filter may, for example, be the maximum of either thecurrent noise measurement or a decayed value of the previous noisefloor.

The output of the noise filter may be an estimate of the current noisefloor level after selecting the highest of a plurality (e.g., 6) ofnoise measurements or samples. The filtered noise floor mayadvantageously include samples collected, captured or measured bothbefore and after a given signal sample is collected, captured ormeasured. Thus, for any sample of a given detection cycle the noisefloor may include noise samples from the given detection cycle, as wellas a next successive detection cycle. The filtered noise floor mayadditionally, or alternatively, include noise samples from one or moresuccessively preceding detection cycles, as well as one or moresuccessfully succeeding detection cycles.

FIG. 7 shows a method 700 of operating the interrogation and detectionsystem 104 according to one illustrated embodiment.

In response to detecting a disconnect of power, the interrogation anddetection system 104 enters a Power OFF mode at 702. For example, thePower OFF mode 702 may be entered when the controller 110 (FIGS. 1 and4) is unplugged or when the power switch on the controller 110 is turnedOFF. In the Power OFF mode 702, the Power LED 434 a and other frontpanel LEDs 434 will be turned OFF (non-emitting). The software 200 isinoperative in the Power OFF mode 702.

In response to detecting an application of power, the interrogation anddetection system 104 enters a Power-Up mode 704. The Power UP mode 704may, for example, in response to the application of power to thecontroller 110 and turning ON the switch on the back of the controller.In the Power-Up mode 704, a Power LED 434 a may be turned ON orilluminated, and may remain ON or illuminated as long as the power isapplied and the switch is in the ON state. In response to entering thePower UP mode 704, the software 200 will perform softwareinitialization, built in tests, and an audio/visual test.

If a fault is detected, the software 200 progresses to a System FaultMode 706. If no faults are detected, the software 200 may turn a SystemReady LED green, and enter a Probe Detection Mode 708.

In the System Fault Mode 706, the software 200 may cause an indicationof the detection of a system fault by blinking a System Ready LED 434 byellow, and/or issuing a sequence of rapid beeps or other sounds. Thecorrective action for the System Fault Mode 706 is to cycle power toreinitiate the Power Up mode 704. Continued failure indicates a failedcontroller 110.

In the Probe Detection Mode 708, the software 200 checks for a probe 112connected to the controller 110. The Probe Detection Mode 708 may beindicated by turning the System Ready LED 434 b green and turning theProbe Ready LED 434 c OFF. If no probe 112 is detected, the software 200remains in the Probe Detection Mode. If a probe 112 is detected, thesoftware 200 progresses to the Probe Initialization Mode 710.

At the start of the Probe Initialization Mode 710, after the detectionof a probe 112, the software 200 may turn the Probe Ready LED 434 cyellow and check for the presence of a fuse in the probe 112. If a fuseis found, the software 200 may attempt to blow the fuse and verify thatthe fuse was correctly blown. After the fuse is blown the software 200may verify that probe 112 is operating within tolerances. The software200 may indicate that the probe 112 is ready by turning the Probe ReadyLED 434 c green. The software 200 may also start a timer which willallow the probe 112 to be disconnected and reconnected to the controllerfor a period to time (e.g., 5 hours) after the fuse is blown.

The controller 110 may determine the adjustments or fine tuning to bemade about the center frequencies or channels during ProbeInitialization Mode 710. In particular, the controller 110 may determinethe particular frequency in each of the frequency bands that elicits theresponse with the highest voltage. The controller may determine such byvarying the capacitance of the LC circuit using the switched capacitorsC33-C36 during the Probe Initialization Mode 710. The particularcombination of switched capacitors C33-C36 which achieved the responsewith the highest voltage may then be automatically employed during aScan Mode 714 (discussed below) to adjust or fine tune about the centerfrequency or channel in each broad band of transmission. Otherapproaches to determining the fine tuning may be employed.

If the software 200 does not successfully complete the ProbeInitialization Mode 710, the software 200 enters an Invalid Probe Mode712. If the software 200 successfully completes the Probe InitializationMode 710, the software 200 progresses to the Scan Mode 714 toautomatically start scanning.

In the Invalid Probe Mode 712, the software 200 may blink the ProbeReady LED 434 c yellow and issues a slow beep pattern.

The Invalid Probe Mode may be entered in response to any of thefollowing conditions: The probe 112 connected to the controller 110 isout of tolerance.

The controller 110 is unable to blow the fuse in the probe 112.

The probe 112 does not have a fuse and more than the set time period haspast (e.g., 5 hours) since a fuse was blown.

The probe 112 does not have a fuse and the controller 110 has beenrestarted.

The probe 112 has been connected to the controller for more than the settime period (e.g., 5 hours).

The probe 112 is detuned due to close proximity to metal.

The corrective action for the Invalid Probe Mode 712 is to remove theinvalid probe 112 and attach a new probe 112 to the controller 110 thatcontains a fuse or to reconnect the probe 112 while holding it in theair at least 2 feet away from large metallic objects.

The software 200 enters the Scan Mode 714 when the probe 112 is readyand the operator presses a Start/Stop button. The software 200 may issuea short three beep pattern via the speaker or beeper 130 when enteringthe Scan Mode 714 to identify the entry to the user.

In the Scan Mode 714, the software 200 may continuously or periodicallyperform the following functions.

Look for response signals from transponders 116

Monitor the Noise Level

Insure the probe 112 is connected and operating correctly

Blink the LED's in a circular pattern

When the operator or user pushes the Start/Stop button or the a scanmaximum time interval (e.g., 4 minute) has been reached, the software200 may issue a short three beep pattern and return to the Probe ReadyMode 716.

When an appropriate response signal from a transponder 116 is detectedwhile in Scan Mode 714, the software 200 may turn ON an amber DETECTLEDs 434 d and/or provide an audible alarm. The alarm may, for example,beep a continuous solid tone as long as the transponder is detected,with a minimum of beep duration of, for instance 0.5 second.

If the software 200 detects the probe 112 is disconnected while in theScan Mode 714, the software 200 enters the Scan Fault Mode 720. In theScan Fault Mode 720, the software 200 may issue a sequence of rapidbeeps and blink ON and OFF the amber DETECT LEDs 434 d. The Scan FaultMode 720 can be cleared by pushing the Start/Stop button. The software200 will automatically clear the Scan Fault Mode 720 after 10 beeps.

While in the Scan Mode 714, if excess noise or loss of transmit signalis detected, the software 200 will progress to the Environment ErrorMode 722. In the Environment Error Mode 722, the software 200 may issueor produce an appropriate indication. For example, the software 200 maycause the production of a sequence of slow beeps and the blinking ON andOFF the green circle LEDs 434 e. The corrective action for theEnvironment Error Mode 722 is to reposition the probe 112 away fromlarge metal objects or sources of electrical interference. The software200 will automatically stop the scan if the environment error conditionlasts for more than a set time or number of beeps (e.g., 5 beeps).

FIG. 8 shows a method 800 of operating an interrogation and detectionsystem, according to one illustrated embodiment. The method 800 may beimplemented by any of the interrogation and detection system embodimentsdiscussed above.

During each of a plurality of detection cycles, the interrogation anddetection system performs a number of acts 802-814. At 802, theinterrogation and detection system receives electromagnetic signals, forexample unmodulated electromagnetic signals, during a noise detectionportion of the detection cycle. The below descriptions will be presentedin terms of unmodulated electromagnetic signals due to the uniquetechnical advantages realized by a system that employs simple resonanttransponders without any on-board memory or storage, and from whichinformation cannot be read from or written to. However, some embodimentsmay employ readable and/or writable transponders, for instance radiofrequency identification (RFID) transponders or tags, which respond witha modulated electromagnetic signal that encodes information in themodulation. The various techniques described herein are applicable tosuch transponders and modulated electromagnetic signals.

At 804, the interrogation and detection system determines a noise valueindicative of a noise level that corresponds to a highest one of anumber N of samples or measurements of the unmodulated electromagneticsignals received during the noise detection portion of the detectioncycle, where the number N is greater than one. At 806, the interrogationand detection system adjusts a signal detection threshold based at leastin part on the determined noise value of at least one of the detectioncycles.

At 808, the interrogation and detection system emits at least oneelectromagnetic interrogation signal during a transmit portion of thedetection cycle. At 810, the interrogation and detection system receivesunmodulated electromagnetic signals during a receive response portion ofthe detection cycle that follows the transmit portion of the detectioncycle.

At 812, the interrogation and detection system determines the presenceor absence of a transponder based at least in part on a number M ofsamples or measurements of the unmodulated electromagnetic signalsreceived during the detection cycle and the adjusted signal detectionthreshold, where the number M is greater than one. A ratio of N:M may beat least equal to 4. N may be equal to about 200 and M may be equal toabout 800.

The interrogation and detection system may determine a noise valueindicative of a noise level based at least in part on the unmodulatedelectromagnetic signals received during the noise detection portion ofthe detection cycle by setting the noise value based on the highest oneof six samples or measurements of the unmodulated electromagnetic signalreceived during the noise detection portion of the detection cycle.

The interrogation and detection system may adjust the signal detectionthreshold by adjusting the signal detection threshold based at least inpart on a first number of determined noise values indicative of a noiselevel during at least one noise detection portion that occurred beforethe receive response portion of a first one of the detection cycles anda second number of determined noise values indicative of a noise levelduring at least one noise detection portion that occurred after thereceive response portion of the first one of the detection cycles.

The interrogation and detection system may adjust the signal detectionthreshold based at least in part on the determined noise value of atleast one of the detection cycles by adjusting the signal detectionthreshold to be approximately twice an average of at least one of thefirst and the second number of determined noise values.

The interrogation and detection system may adjust the signal detectionthreshold based at least in part on the determined noise value of atleast one of the detection cycles by adjusting the signal detectionthreshold to be approximately twice a greatest one of at least one ofthe first and the second number of determined noise values.

The interrogation and detection system may determine the presence orabsence of a transponder by comparing a maximum value of a plurality ofmatched filter outputs with the adjusted signal threshold.

The interrogation and detection system may adjust the signal detectionthreshold based at least in part on the determined noise value of atleast one of the detection cycles by adjusting the signal detectionthreshold to be approximately twice the determined noise value.

The interrogation and detection system may adjust the signal detectionthreshold based at least in part on the determined noise value of atleast one of the detection cycles includes adjusting the signaldetection threshold to be the large of approximately twice thedetermined noise value or a defined threshold value. The definedthreshold value may for example be approximately 0.5 mV.

In some embodiments, the interrogation and detection system determinesif an output of at least one matched filter during the noise detectionportion of the detection cycle exceeds a noise fault thresholdindicative of a noise fault.

In some embodiments, the interrogation and detection system determinesif the output of the at least one matched filter during the noisedetection portion of the detection cycle exceeds the noise faultthreshold for a defined period of time. The interrogation and detectionsystem may terminates the detection cycle in response to the output ofthe at least one matched filter exceeding the noise fault threshold forthe defined period of time.

The interrogation and detection system may convert the receivedsignal(s) from the time domain to the frequency domain spectrum. Theinterrogation and detection system may, for example, perform a Fouriertransform, for instance a fast Fourier transform such as a 256 pointfast Fourier transform. Suitable algorithms and/or sets of software codefor performing such are available or can be written.

The interrogation and detection system may search the frequency domainspectrum to determine the object with the strongest resonance in adefined frequency band. For example, the interrogation and detectionsystem may search the frequency domain spectrum from about 120 kHz toabout 175 kHz. An amplitude of the resonant object may be computed asthe sum of the resonant power plus and minus 2 fast Fourier transformbins from the peak resonance frequency. This approach may provide a moreaccurate measurement of power than simply using the peak value. Thefrequency of the resonant object may be computed using an interpolationapproach. This approach may provide a more accurate determination ofresonant frequency than simply using the fast Fourier bin number.

The interrogation and detection system may determine the presence orabsence of a transponder based at least in part on a frequency of theunmodulated electromagnetic signals received during the detection cyclebeing within a defined frequency range. The defined frequency range mayextend from about 137 kHz to about 160 kHz.

The interrogation and detection system may determine a Q value (i.e.,Quality factor) of the resonant object from a signal decay slope for thereceived unmodulated electromagnetic signal(s) returned by the resonantobject. The interrogation and detection system may, for example, usemultiple windows, for instance five (5) window positions may providesuitable results.

The interrogation and detection system may determine the presence orabsence of a transponder based at least in part on a Q value of theunmodulated electromagnetic signal(s) received during the detectioncycle. The interrogation and detection system may preferably employ theQ value determination in conjunction with determination based on thefrequency and on the determination based on the adjusted signaldetection threshold.

In some embodiments, the interrogation and detection system determinesthe presence or absence of a transponder is based at least in part on aQ value of the unmodulated electromagnetic signals received during thedetection cycle being at least equal to a threshold Q value. Thethreshold Q value may be 35, for example. The interrogation anddetection system may preferably employ the Q value determination inconjunction with determination based on the frequency and on thedetermination based on the adjusted signal detection threshold.

Consequently, tag detection may advantageously be based on the receivedunmodulated electromagnetic signal(s) satisfying all threeconditions: 1) measured amplitude is above a threshold, which may be anadjustable threshold, 2) measured frequency is between a lower limit andan upper limit, and 3) measured Q value is above a minimum Q threshold.Interference, for example from RFID tags or EKG cables, are rejectedwhen any of the following three conditions are satisfied: a) measuredfrequency is below the lower frequency limit, b) measured frequency isabove the upper frequency limit, or c) measured Q value is below thethreshold Q value. Such may provide significantly superior results overprevious approaches, preventing false positives which could otherwisecause a patient to remain open for longer period of time during surgeryand tie up hospital personnel and resources.

FIG. 9 shows a graph 900 of a simulated transponder response signal 902and a noise signal 904. The inexpensive transponders usable withembodiments disclosed herein typically have a relatively large variationin the frequency of signals they emit, making it difficult to accuratelydetect the signals returned by the transponders. This may beparticularly difficult in some environments which are noisy with respectto the particular resonant frequencies of the transponders. For example,operating rooms may have one or more electronic medical devices thatemit RF noise that is harmonically synchronous with the response signalsreceived from the transponders. Consequently, even though the responsessignals may be received synchronously with the transmitted interrogationsignals, noise that is harmonically synchronous with the responsesignals may still be high if the peaks of the noise occur at times theinterrogation and detection system is expecting to see response signalsfrom a transponder.

The transponder response signal 902 may, for example, be a nominalperiodic signal centered around a particular frequency (e.g., 136 kHz,145 kHz, 154 kHz, etc.). The noise signal 904 may be emitted from anelectronic medical device located proximate to the interrogation anddetection system 104 (FIG. 1), for example. In this illustration, theamplitude of the noise signal 904 is much greater than the amplitude ofthe transponder response signal 902. As shown, at a point 906 in timethe noise signal 904 is at a peak and the transponder response signal902 is near its zero crossing. If the interrogation and detection system104 were to obtain a sample at the point 906 the noise signal 904 wouldmask the transponder response signal 902. Conversely, at points 908 and910, the noise signal 904 is at or close to its zero crossing while thetransponder response signal 902 is near its peak. If the interrogationand detection system 104 can sample the simulated response signal 902 attimes when the noise signal 904 is at its zero crossing or at a lowamplitude, it is possible for the interrogation and detection system todetect a transponder through the noise signal 904 (or “noise floor”)that is many times greater than the transponder response signal 902.

To accomplish this, in some embodiments the scanning process for eachantenna 306 (FIG. 1) or coil is broken down into N_(SS) subsample scancycles for each transmit frequency. Each of the subsample scan cyclesincludes one or more interrogation cycles. As discussed in furtherdetail below, each of the interrogation cycles in a particular one ofthe N_(SS) subsample scan cycles is shifted forward in time a fractionof the period (T) of a nominal expected transponder response signal 902to provide N_(SS) opportunities to avoid harmonic noise beingsynchronous in time with the desired transponder response signal.

FIG. 10 illustrates timing for a single interrogation cycle 1010 in anembodiment that utilizes the aforementioned subsample scan cycles,according to one illustrated embodiment. Each of the N_(SS) subsamplescan cycles may include one or more interrogation cycles 1010, asdiscussed below. The custom logic in the FPGA 508 (FIG. 5) generates thetiming and control signals for each interrogation cycle 1010. During atransmit portion 1010 a of the interrogation cycle 1010, the logic ofthe FPGA 508 drives transistor control lines to generate the transmitsignal. The FPGA logic controls the frequency of the transmit signal. Insome embodiments, the transmit portion 1010 a has a duration of 200microseconds (μs), for example. During a dump portion 1010 b of theinterrogation cycle 1010, the logic of the FPGA 508 drives a gate of adump TRIAC to quickly drain the transmit energy from the antenna 306 toallow detection of the response signal from the transponder 116, if any.In some embodiments, the dump portion 1010 b has a duration of 10 μs,for example. A recovery portion 1010 c of the interrogation cycle 1010allows receive filters and amplifiers to recover from the transmittedsignal before detecting the response signal from the transponder 116, ifany. The recovery portion 1010 c may have a duration of 100 μs, forexample. During a receive response portion 1010 d of the interrogationcycle 1010, the FPGA 508 controls the signal ADC 128 to sample theresponse signal from the transponder 116, if any. The signal ADC 128may, for example, sample at a 1 MHz sample rate (i.e., 1 sample per μs)with a 12-bit resolution. In some embodiments, the receive responseportion 1010 d has a duration of 512 μs, such that the signal ADC 128obtains 512 measurements at the 1 MHz sample rate during the receiveresponse portion 1010 d. A skip portion 1010 e of the interrogationcycle 1010 may be provided during which time measurements from thesignal ADC 128 are skipped or ignored. In some embodiments the skipportion 1010 e has a duration of 40 μs. The timing of the receiveresponse portion 1010 d may be such that the transponder response signalis synchronous to the transmit time.

A subsample scan cycle delay period 1010 f of the interrogation cycle1010 has a unique duration for interrogation cycles associated with aparticular one of the N_(SS) subsample scan cycles. Interrogation cyclesassociated with different ones of the N_(SS) subsample scan cycles mayhave subsample scan cycle delay periods 1010 f having differingdurations. In some embodiments, the subsample scan cycle delay period1010 f associated with respective ones of the N_(SS) subsample scancycles may be approximately a fraction of the period (T) of the expectedtransponder response signal 902 (FIG. 9). For example, the subsamplescan cycle delay periods 1010 f for interrogation cycles associated withsubsample scan cycles 1 to N_(SS) may be approximately:

(0/N_(SS))*T for interrogation cycles of subsample scan cycle 1;

(1/N_(SS))*T for interrogation cycles of subsample scan cycle 2;

(2/N_(SS))*T for interrogation cycles of subsample scan cycle 3;

. . . .

((N_(SS)−1)/N_(SS))*T for interrogation cycles of subsample scan cycleN_(SS).

Thus, the period (T) of the expected transponder response signal isdivided into N_(SS) start times, with each of the N_(SS) subsample scancycles being associated with a different one of the start times.

FIG. 11A is a timing diagram 1100 illustrating an overall instrumentscan cycle 1102, according to one illustrated embodiment. The instrumentscan cycle 1102 may be implemented by the interrogation and detectionsystem 104 to scan for one or more resonant transponders. The instrumentscan cycle 1102 may have a duration between a start time and a stop timethat is less than about 20 seconds (e.g., two seconds, five seconds, 10seconds, 15 seconds, etc.) so that the user operating the interrogationand detection system 104 does not need to wait an extended period oftime to perform a scan operation. The instrument scan cycle 1102 may beexecuted one or more times during the Scan Mode of the interrogation anddetection system 104. As discussed in further detail below, eachinstrument scan cycle 1102 may include one or more coil scan cycles,which may include one or more frequency specific sample cycles, whichmay include one or more subsample scan cycles, which may include one ormore interrogation cycles.

The instrument scan cycle 1102 includes a number N_(COILS) of coil scancycles 1104, one coil scan cycle for each of N_(COILS) present in theinterrogation and detection system 104. For example, the system 104 mayinclude three antenna coils (N_(COILS)=3), mutually orthogonal to eachother, such that each instrument scan cycle 1102 includes three coilscan cycles 1104. In some embodiments the system 104 may include sixantenna coils (N_(COILS)=6), or a greater or fewer number of antennacoils. In some embodiments, the system 104 includes a single coil(N_(COILS)=1), such that only a single coil scan cycle 1104 is performedduring each instrument scan cycle 1102.

FIG. 11B is a timing diagram 1106 illustrating a cycle for one of thecoil scan cycles 1104 shown in FIG. 11A, according to one illustratedembodiment. The coil scan cycle 1104 includes a number N_(FREQ) offrequency specific sample cycles 1108, one for each transmit frequencyto be used by the interrogation and detection system 104. The numberN_(FREQ) of frequency specific sample cycles 1108 may be any suitablevalue, such as one, two, five, eight, etc. For example, in someembodiments the interrogation and detection system 104 may transmitinterrogation signals at 139 kHz, 145 kHz, and 154 kHz during frequencyspecific sample cycle 1, frequency specific sample cycle 2, andfrequency specific sample cycle 3, respectively. In some embodiments,the interrogation and detection system 104 may transmit at a singlefrequency, such that only a single frequency specific sample cycle 1108is performed during each coil scan cycle 1104.

FIG. 11C is a timing diagram 1110 illustrating a cycle for one of thefrequency specific sample cycle 1108, according to one illustratedembodiment. The frequency specific sample cycle 1108 includes a numberN_(SS) of subsample scan cycles 1112, one for each subsample to becollected by the interrogation and detection system 104. As used herein,a subsample may refer to measurements obtained during a subsample scancycle. As discussed above, the number N_(SS) of subsample scan cycles1112 in each frequency specific sample cycle may be any suitable value,such as two, five, 10, 15, etc. As discussed above, each of the N_(SS)subsample scan cycles has a unique subsample scan cycle delay periodassociated therewith. The subsample scan cycle delay periods for each ofthe N_(SS) subsample scan cycles are applied during respectiveinterrogation cycles associated with the respective subsample scancycles.

FIG. 11D is a timing diagram 1114 illustrating one cycle of one of thesubsample scan cycles 1112, according to one illustrated embodiment. Thesubsample scan cycle 1112 includes a number N_(I) of interrogationcycles 1010 (FIG. 10). As discussed below with reference to the exampleshown in FIG. 12, each of the N_(I) interrogation cycles 1010 has asubsample scan cycle delay period 1010 f associated with one of theparticular subsample scan cycles 1112. In other words, interrogationcycles 1 to N_(I) for one of the subsample scan cycles 1112 all have thesame subsample scan cycle delay period 1010 f. The number ofinterrogation cycles (N_(I)) per subsample scan cycle 1112 may be anysuitable value, such as 10, 250, 500, or 1000 interrogation cycles persubsample scan cycle.

FIG. 12 illustrates a timing diagram 1200 for performing N_(SS)subsample scan cycles 1202 (labeled subsample scan cycles 1-7) to obtainN_(SS) subsamples, where N_(SS) equals seven in this illustratedexample. In this embodiment, each of the subsample scan cycles 1-7include 250 interrogation cycles 1010 (FIG. 10). Each of theinterrogation cycles is designated as I_(X-Y), where X is the subsamplescan cycle with which the interrogation cycle is associated and Y is thenumber of the interrogation cycle within the subsample scan cycle. Forexample, I₂₋₃ represents the third interrogation cycle 1010 in subsamplescan cycle 2. During a particular frequency specific sample cycle 1108(FIG. 11) of a coil scan cycle 1104, the interrogation and detectionsystem 104 performs subsample scan cycles 1-7 using a particular antennacoil (e.g., coil 306 a of FIG. 3B) by sequentially executinginterrogation cycles I₁₋₁ to I₁₋₂₅₀, I₂₋₁ to I₂₋₂₅₀, I₃₋₁ to I₃₋₂₅₀,I₄₋₁ to I₄₋₂₅₀, I₅₋₁ to I₅₋₂₅₀, I₆₋₁ to I₆₋₂₅₀, and I₇₋₁ to I₇₋₂₅₀, fora total of 1750 interrogation cycles, in this embodiment. Table 2 belowshows the approximate subsample scan cycle delay periods 1010 f forinterrogation cycles 1010 within each of the subsample scan cycles 1-7.

TABLE 2 Subsample Scan Cycle Subsample Scan Cycle Delay Period for DelayPeriod: Response Subsample Scan Interrogation Cycles in Signal at 145kHz Cycle Subsample Scan Cycle (T = 6.9 μs) 1 (0/7) * T   0 μs 2 (1/7) *T ~1 μs 3 (2/7) * T ~2 μs 4 (3/7) * T ~3 μs 5 (4/7) * T ~4 μs 6 (5/7) *T ~5 μs 7 (6/7) * T ~6 μs

In the illustrated embodiment, the subsample scan cycle delay periods1010 f are evenly spaced across the duration of the period (T) of theexpected transponder response signal. For example, for a transponderresponse signal expected to have a center frequency of about 145 kHz,the period T is approximately 6.9 μs. Accordingly, interrogation cyclesof a next successive subsample scan cycle has a subsample scan cycledelay period 1010 f that is about 1/7 of the transponder response signalperiod T greater than interrogation cycles of a previous successivesubsample scan cycle. As an example, the subsample scan cycle delayperiod 1010 f for interrogation cycles I₄₋₁ to I₄₋₂₅₀ of subsample scancycle 4 is three (3) μs and the subsample scan cycle delay period 1010 ffor interrogation cycles I₅₋₁ to I₅₋₂₅₀ of subsample scan cycle 5 isfour (4) μs. By utilizing seven different subsample scan cycle delayperiods 1010 f spread across the duration of the period T of theexpected transponder response signal, the probability of a sampling at atime of low harmonically synchronous noise and high transponder responsesignal is increased. In some embodiments, more or less than sevensubsample scan cycles may be used.

In some embodiments, the subsample scan cycle delay periods 1010 f ofthe interrogation cycles may be different fractions of the period (T) ofthe expected transponder response signal, offset by one or more periodsT. For example, in some embodiments with four subsample scan cycles,interrogation cycles of a subsample scan cycle 1 may have a subsamplescan cycle delay period of T (i.e., (0/4)*T+T), such that the subsamplescan cycle delay period is offset by one period T relative to theexample provided in Table 2. Similarly, interrogation cycles of asubsample scan cycle 2 may have a subsample scan cycle delay period of(5/4)*T (i.e., (1/4)*T+T=(5/4)*T), interrogation cycles of a subsamplescan cycle 3 may have a subsample scan cycle delay period of (6/4)*T(i.e., (2/4)*T+T=(6/4)*T), and interrogation cycles of a subsample scancycle 4 may have a subsample scan cycle delay period of (7/4)*T (i.e.,(3/4)*T+T=(7/4)*T). Importantly, the subsample scan cycle delay periodsfor the interrogation cycles in respective subsample scan cycles aredifferent fractions of the expected transponder response signal. Othervalues for the subsample scan cycle delay periods may be used to obtainsamples at different start times within the period T of the expectedtransponder response signal.

FIG. 13 shows a method 1300 of operating an interrogation and detectionsystem to implement a coil scan cycle 1104 (FIGS. 11A-D), according toone illustrated embodiment. The method 1300 may be implemented by any ofthe interrogation and detection system embodiments discussed above. Themethod 1300 may be used to collect subsamples using the subsample scancycles including the interrogation cycles 1010 illustrated in FIGS. 10and 12 for a single antenna coil. The method 1300 may be repeated forinterrogation and detection systems utilizing a plurality of antennacoils (e.g., three mutually orthogonal antenna coils).

The method starts at 1302. The method 1300 may, for example, start whenan interrogation and detection system enters the Scan Mode 714 (FIG. 7).At 1304, the interrogation and detection system initializes a controlvariable FREQUENCY_COUNT that may be used for comparison with a numberof frequency bands to be used in the coil scan cycle (i.e., the numberof frequency specific sample cycles 1108). In some embodiments, morethan one frequency band may be used during the coil scan cycle. Forexample, a first interrogation signal may be centered around 139 kHz, asecond interrogation signal may be centered around 145 kHz, and a thirdinterrogation signal may be centered around 154 kHz, for a total ofthree frequency specific sample cycles. Other center channels orfrequencies may for example be 136 kHz, 142 kHz, 148 kHz, and or 151kHz, or any other frequency suitable for exciting the transponder toresonate.

At 1306, the interrogation and detection system initializes a controlvariable SUBSAMPLE_COUNT. This control variable may be used during themethod 1300 for comparison with a number of subsample scan cycles N_(SS)to be executed by the interrogation and detection system. In the exampleshown in FIG. 12, the number of subsample scan cycles N_(SS) is seven,but more or less subsample scan cycles may be used depending on how manydivisions or start times in the period T of the expected transponderresponse signal are to be used. If N_(SS) is relatively small, theprobability of sampling at a time of low harmonically synchronous noiseis reduced since the number of opportunities is reduced. If N_(SS) isrelatively large, the probability of sampling at a time of lowharmonically synchronous noise is increased, but a tradeoff is that thetotal time for the coil scan cycle 1104 may also be increased.

At 1308, the interrogation and detection system initializes a controlvariable INTERROGATION_COUNT. This control variable may be used duringthe method 1300 for comparison with the number N_(I) of interrogationcycles 1010 in each subsample scan cycle. In the example of FIG. 12,each subsample scan cycle includes 250 interrogation cycles 1010. Moreor less interrogation cycles per subsample scan cycle may be used.

At 1310, the interrogation and detection system begins a firstinterrogation cycle (interrogation cycle 1) for a first subsample scancycle (subsample scan cycle 1) by emitting an electromagneticinterrogation signal centered at first frequency (frequency specificsample cycle 1) during a transmit portion 1010 a of the interrogationcycle (see FIGS. 10 and 11). At 1312, the interrogation and detectionsystem receives unmodulated electromagnetic signals during a receiveresponse portion 1010 d of the interrogation cycle that follows thetransmit portion 1010 a of the interrogation cycle. As discussed abovewith reference to FIG. 10, the interrogation cycle may include a dumpportion 1010 b, recovery portion 1010 c, and/or a skip portion 1010 ebetween the transmit portion 1010 a and the receive response portion1010 d. The timing of the receive response portion 1010 d may be suchthat the expected transponder response signal is synchronous or coherentwith the transmit portion 1010 a to improve the likelihood that peaks ofthe transponder response signal are detected. During the receiveresponse portion 1010 d of the interrogation cycle, the FPGA 508controls the signal ADC 128 to sample the response signal from thetransponder. The signal ADC 128 may, for example, obtain 512measurements in 512 μs by sampling at a 1 MHz sample rate (i.e., 1sample per μs). In some embodiments the signal ADC 128 may sample atdifferent rates and may obtain more or less measurements during eachreceive response portion 1010 d.

At 1314, the interrogation and detection system waits a subsample scancycle delay period 1010 f, which in some embodiments is a fraction ofthe period T of the expected transponder response signal, beforestarting the next interrogation cycle at 1310. The subsample scan cycledelay period may be approximately equal to ((SUBSAMPLE_COUNT−1)/N_(SS))times the period (T) of the expected transponder response signal, insome embodiments. Thus, for interrogation cycles associated withsubsample scan cycle 1, the subsample scan cycle delay period isapproximately zero seconds (i.e., (0/N_(SS))*T=0). For interrogationcycles associated with subsample scan cycle 2, the subsample scan cycledelay period is approximately equal to (1/N_(SS))*T, and so on asdiscussed above.

At 1316, the interrogation and detection system increments the controlvariable INTERROGATION_COUNT. At 1318, the interrogation and detectionsystem compares the value of INTERROGATION_COUNT to the number ofinterrogation cycles N_(I) per subsample scan cycle. The interrogationand detection system thus continues to loop through acts 1310-1314(i.e., interrogation cycles) until all of the interrogation cycles insubsample scan cycle 1 have been executed. The number of interrogationcycles per subsample scan cycle may be any suitable value, such as 1,100, 250, 500, 2000, etc.

Once all of the interrogation cycles for subsample scan cycle 1 havebeen executed (i.e., decision 1318=YES), the interrogation and detectionsystem increments the control variable SUBSAMPLE_COUNT at 1320, andcompares its value to the number of subsample scan cycles N_(SS) at1322. Thus, similar to the acts for subsample scan cycle 1, theinterrogation and detection system executes the acts 1310-1314 forsubsample scan cycle 2 to subsample scan cycle N_(SS) to complete atotal of N_(SS) subsample scan cycles and collect N_(SS) subsamples.

Once all of the interrogation cycles for each of the subsample scancycles 1 to N_(SS) have been executed (i.e., decision 1322=YES), theinterrogation and detection system increments the control variableFREQUENCY_COUNT at 1324 and compares its value to the number of transmitfrequencies (N_(FREQ)) at 1326. If the number of transmit frequenciesN_(FREQ) is greater than one, the interrogation and detection systemrepeats the acts discussed above to perform N_(SS) subsample scan cyclesat each of the number N_(FREQ) of transmit frequencies for a total ofN_(FREQ) frequency specific sample cycles.

The method 1300 may terminate at 1328 until started again. As discussedabove, the method 1300 may repeat for one or more additional antennacoils of the interrogation and detection system. The method 1300 maycontinually repeat when the interrogation and detection system is in theScan Mode. Alternatively or additionally, the method 1300 may runconcurrently with other methods or processes.

FIG. 14 shows a method 1400 of operating an interrogation and detectionsystem to execute an instrument scan cycle 1102 (FIG. 11), according toone illustrated embodiment. The method 1400 may be implemented by any ofthe interrogation and detection system embodiments discussed above. Themethod 1400 may be used to collect subsamples by performing subsamplescan cycles using the interrogation cycles illustrated in FIGS. 10 and12.

The method starts at 1402. The method 1400 may, for example, start whenan interrogation and detection system enters the Scan Mode 714 (FIG. 7).At 1404, the interrogation and detection system initializes a controlvariable COIL_COUNT. This control variable may be used during the method1400 for comparison with a number of coils (N_(COILS)) included in theinterrogation and detection system. For example, in some embodiments theinterrogation and detection system may include a plurality of coils orantennas that may be used to scan for transponders. In some embodiments,the interrogation and detection system may include a plurality of coilsspaced apart from each other that are each designed to detecttransponders in different physical locations. For example, in someembodiments six coils may be spaced apart in or on a mat positionedunder a patient on a patient support structure. The six coils may beused to detect transponders at different locations proximate to thepatient's body. In some embodiments, multiple coils may be provided totransmit or receive signals in multiple directions (e.g., x-, y-, andz-directions).

At 1406, the interrogation and detection system performs a coil scancycle 1104 (FIG. 11A) to detect transponders using a first coil. Theinterrogation and detection system may execute this act using the method1300 of FIG. 13 discussed above to perform a coil scan cycle 1104, whichmay include N_(FREQ) frequency specific sample cycles, each of which mayinclude N_(SS) subsample scan cycles, each of which may include N_(I)interrogation cycles. At 1408, the interrogation and detection systemincrements the control variable COIL_COUNT and compares its value to thenumber of coils at 1410. If the interrogation and detection subsystemincludes additional coils, the system sequentially performs coil scancycles 1104 in round robin fashion for each of the coils to scan fortransponders.

The method 1400 may terminate at 1412 until started again. The method1400 may continually repeat when the interrogation and detection systemis in the Scan Mode. Alternatively or additionally, the method 1400 mayrun concurrently with other methods or processes.

FIG. 15 shows a method 1500 of operating an interrogation and detectionsystem to execute one or more instrument scan cycles 1102 (FIG. 11),according to one illustrated embodiment. The method 1500 may beimplemented by any of the interrogation and detection system embodimentsdiscussed above. The method 1500 may be used to collect subsamples byperforming subsample scan cycles using the interrogation cyclesillustrated in FIGS. 10 and 12.

The method 1500 begins at 1502. At 1504 the interrogation and detectionsystem may receive a scan mode selection from a user (e.g., via theconsole 110). In some embodiments, a graphical user interface of theconsole 110 may present a prompt to the user requesting a selection of ascan mode. In some embodiments, the system may automatically select ascan mode for the user. In this embodiment, the interrogation anddetection system is configured to provide at least two different typesof instrument scan cycles: a static scan and a dynamic scan. During astatic scan, the user maintains the probe 112 in a substantially fixedposition relative to the patient 108. For example, in a child deliverymedical setting, the user may position the body portion 302 of the probe112 near the top of the patient's pelvic bone when the patient is in thelithotomy position to scan for detection of objects (e.g., retainedsponges). During a dynamic scan, the user may move the probe 112 tovarious locations to scan for detection of objects. For example, in thedynamic instrument scan cycle mode, the user may move the probe 112 neara trash can, near portions of the patient's body, near a drape bag,and/or near other areas in a medical facility to scan for objects (e.g.,so that such objects may be counted).

If the user has selected a static scan (i.e., decision 1506=YES), theinterrogation and detection system executes one or more staticinstrument scan cycles at 1508. If the user has selected a dynamic scan(i.e., decision 1510=YES), the interrogation and detection systemexecutes one or more dynamic instrument scan cycles at 1512.

The static instrument scan cycle and the dynamic instrument scan cyclediffer by the number of subsamples obtained. The time available for thedynamic instrument scan cycle is less than the time available for thestatic instrument cycle because, in the dynamic scan cycle mode, theuser is constantly moving the probe 112 relative to a transponder thatis to be detected. Thus, to provide a relatively fast scan, in someembodiments only a single frequency specific sample cycle 1108 (FIGS.11B and 11C) with four subsample scan cycles 1112 (FIGS. 11C and 11D)are executed in the dynamic instrument scan cycle mode. This is incontrast to the static instrument scan cycle, which in some embodimentsutilizes two or more frequency specific sample cycles 1108 and seven ormore subsample scan cycles 1112 per frequency specific sample cycle.

In operation, the medical provider 102 may operate the interrogation anddetection system in both instrument scan cycle modes after a medicalprocedure. For example, the user may operate the interrogation anddetection system in the static scan cycle mode to first detect whetherany objects are retained in the patient, and then operate the system inthe dynamic scan cycle mode to detect whether any objects are located insurrounding areas (e.g., trash cans, drape bags, etc.).

As discussed above, in some embodiments the dynamic scan mode includes asingle frequency specific sample cycle 1108 (FIGS. 11B and 11C) thatincludes four subsample scan cycles 112. Thus, the instrument scan cycle1102 in the dynamic mode includes sequentially performing a coil scancycle 1104 (FIG. 11A) for each of the three orthogonal coils 306 a, 306b, and 306 c, where each coil scan cycle includes one frequency specificsample cycle 1108 that includes four subsample scan cycles 1112.

In some embodiments, the static scan mode includes two frequencyspecific sample cycles 1108 that each include seven subsample scancycles 1112. Thus, the instrument scan cycle 1102 in the static modeincludes sequentially performing a coil scan cycle 1104 for each of thethree orthogonal coils 306 a, 306 b, 306 c, where each coil scan cycleincludes two frequency specific sample cycles 1108 that each includeseven subsample scan cycles 1112.

In some embodiments, a single subsample scan cycle 1112 may have aduration of approximately 216 milliseconds. Continuing with the examplediscussed above, a single dynamic instrument scan cycle may have aduration of about 2.6 seconds (i.e., 216 milliseconds per subsample scancycle, 4 subsample scan cycles per frequency specific sample scan, 1frequency specific sample scan per coil, and 3 orthogonal coils). Asingle static instrument scan cycle may have a duration of approximately9.1 seconds (i.e., 216 milliseconds per subsample scan cycle, 7subsample scan cycles per frequency specific sample scan, 2 frequencyspecific sample scans per coil, and 3 orthogonal coils). The durationsof the static and dynamic instrument scan cycles may be modified to suita particular application, recognizing the tradeoff between scan time andthe number of samples collected.

The method 1500 terminates at 1514 until started again. The method 1500may start again, for example, when the user makes a selection of one ofthe dynamic scan cycle mode or the static scan cycle mode.

FIG. 16 shows a method 1600 of operating an interrogation and detectionsystem, according to one illustrated embodiment.

At 1602, the interrogation and detection system determines the presenceor absence of a transponder based at least in part on at least one ofthe subsamples obtained by performing the method 1300 and/or the method1400 discussed above (FIGS. 13 and 14).

As discussed above, the signal ADC 128 (FIG. 5) converts the signalreceived from the transponder, if any, from analog to digital. Suchconversion may, for example, be performed at a sampling rate of 1 MHzwith a 12-bit data resolution. In the example shown in FIG. 12,subsample scan cycles 1-7 each include 250 interrogation cycles, and thesignal ADC 128 obtains 512 measurements per interrogation cycle. Thesampled ADC data for each subsample scan cycle may be accumulatedtogether or integrated to compute the total summed response signalreceived from the transponder 116, if any, for each subsample.

In some embodiments, the accumulated or integrated received signal foreach subsample is matched filtered with both in-phase and quadraturereference signals to determine the signal magnitude. The receivedresponse signal may be matched filtered with a plurality of referencesignals, for example with the seven reference signals, for instance asshown in Table 1 above. Some embodiments may employ matched filteringbefore accumulating or integrating the received signal.

For each subsample collected, the maximum value for the matched filters(e.g., seven matched filters) with active transmit may be compared withan adjusted detection threshold. If the maximum value is greater thanthe detection threshold for one or more subsamples, then a responsesignal from a transponder is considered as having been detected, andappropriate action is taken, such as discussed above with reference toFIG. 7. In some embodiments, a value greater than the detectionthreshold for two or more subsamples is required before a transponder isconsidered to have been detected.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other transponders andinterrogation and detection systems, not necessarily the exemplarysurgical object transponders and interrogation and detection systemsgenerally described above.

For instance, the foregoing detailed description has set forth variousembodiments of the devices and/or processes via the use of blockdiagrams, schematics, and examples. Insofar as such block diagrams,schematics, and examples contain one or more functions and/oroperations, it will be understood by those skilled in the art that eachfunction and/or operation within such block diagrams, flowcharts, orexamples can be implemented, individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. In one embodiment, the present subject matter may beimplemented via Application Specific Integrated Circuits (ASICs).However, those skilled in the art will recognize that the embodimentsdisclosed herein, in whole or in part, can be equivalently implementedin standard integrated circuits, as one or more computer programsrunning on one or more computers (e.g., as one or more programs runningon one or more computer systems), as one or more programs running on oneor more controllers (e.g., microcontrollers) as one or more programsrunning on one or more processors (e.g., microprocessors), as firmware,or as virtually any combination thereof, and that designing thecircuitry and/or writing the code for the software and or firmware wouldbe well within the skill of one of ordinary skill in the art in light ofthis disclosure.

In addition, those skilled in the art will appreciate that themechanisms of taught herein are capable of being distributed as aprogram product in a variety of forms, and that an illustrativeembodiment applies equally regardless of the particular type of signalbearing media used to actually carry out the distribution. Examples ofsignal bearing media include, but are not limited to, the following:recordable type media such as floppy disks, hard disk drives, CD ROMs,digital tape, and computer memory; and transmission type media such asdigital and analog communication links using TDM or IP basedcommunication links (e.g., packet links).

The various embodiments described above can be combined to providefurther embodiments. U.S. Provisional Patent Application Ser. No.61/056,787, filed May 28, 2008; U.S. Provisional Patent Application Ser.No. 61/091,667, filed Aug. 25, 2008; U.S. Provisional Patent ApplicationNo. 60/811,376 filed Jun. 6, 2006; U.S. Pat. No. 6,026,818, issued Feb.22, 2000; U.S. Patent Publication No. U.S. 2004/0250819, published Dec.16, 2004; U.S. provisional patent application Ser. No. 60/811,376, filedJun. 6, 2006 and U.S. non-provisional patent application Ser. No.11/743,104, filed May 1, 2007, are incorporated herein by reference, intheir entirety. Aspects of the embodiments can be modified, ifnecessary, to employ systems, circuits and concepts of the variouspatents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A transponder detection device, comprising:a coil form that includes three coil support channels, each of the coilsupport channels curved about a respective primary axis and curved abouta respective secondary axis orthogonal to the respective primary axis,the primary axes orthogonal to one another, the coil form having ahollow interior center; a first antenna element including a firstelectrical wire wound around a first one of the three coil supportchannels, the first antenna element arranged to transmit and receivesignals generally in a first coordinate direction; a second antennaelement including a second electrical wire wound around a second one ofthe three coil support channels over the first electrical wire, thesecond antenna element arranged to transmit and receive signalsgenerally in a second coordinate direction orthogonal to the firstcoordinate direction; and a third antenna element including a thirdelectrical wire wound around a third one of the three coil supportchannels over the first electrical wire and the second electrical wire,the third antenna element arranged to transmit and receive signalsgenerally in a third coordinate direction orthogonal to the firstcoordinate direction and the second coordinate direction.
 2. Thetransponder detection device of claim 1, further comprising: a processoroperatively coupled to the first antenna element, the second antennaelement, and the third antenna element; and a nontransitoryprocessor-readable medium communicatively coupled to the processor andthat stores at least one of instructions or data executable by theprocessor, which cause the processor to: independently control each ofthe first antenna element, the second antenna element and the thirdantenna element to emit wideband interrogation signals; receive thereturn signals from any resonant tag elements; and determine from areceipt of the return signals whether any of the resonant tag elementsare present in a work area.
 3. The transponder detection device of claim2, wherein the nontransitory processor-readable medium stores furtherinstructions or data executable by the processor, which cause theprocessor to: control each of the first antenna element, the secondantenna element and the third antenna element to emit the widebandinterrogation signals in time-wise succession during a transmit portionof respective transmit and receive cycles, and control each of the firstantenna element, the second antenna element and the third antennaelement to not emit the wideband interrogation signals during a receiveportion of respective transmit and receive cycles.
 4. The transponderdetection device of claim 2, wherein the nontransitoryprocessor-readable medium stores further instructions or data executableby the processor, which cause the processor to: receive a selection ofat least one of a dynamic scan mode and a static scan mode; in responseto receiving a selection of the static scan mode, control each of thefirst antenna element, the second antenna element and the third antennaelement to emit the wideband interrogation signals according to a staticinstrument scan cycle having a static instrument scan cycle duration;and in response to receiving a selection of the dynamic scan mode,control each of the first antenna element, the second antenna elementand the third antenna element to emit the wideband interrogation signalsaccording to a dynamic instrument scan cycle having a dynamic instrumentscan cycle duration that is less than the static instrument scan cycleduration.
 5. The transponder detection device of claim 4, wherein, inresponse to receiving a selection of the static scan mode, theinstructions or data further cause the processor to control each of thefirst antenna element, the second antenna element and the third antennaelement to the emit wideband interrogation signals centered on a firstfrequency, and further control each of the first antenna element, thesecond antenna element and the third antenna element to emit thewideband interrogation signals centered on a second frequency, thesecond frequency different from the first frequency.
 6. The transponderdetection device of claim 4, wherein the static instrument scan cycleduration is less than fifteen (15) seconds and the dynamic instrumentscan cycle duration is less than five (5) seconds.
 7. The transponderdetection device of claim 2, wherein the nontransitoryprocessor-readable medium stores further instructions or data executableby the processor, which cause the processor to: determine from a receiptof any of the return signals whether any of the resonant tag elementsare present in the work area based at least in part on a frequency ofthe return signals received being within a defined frequency range. 8.The transponder detection device of claim 2, wherein the nontransitoryprocessor-readable medium stores further instructions or data executableby the processor, which cause the processor to: determine whether any ofthe resonant tag elements are present in the work area based at least inpart on a Q value of the return signals received.
 9. The transponderdetection device of claim 2, wherein the nontransitoryprocessor-readable medium stores further instructions or data executableby the processor, which cause the processor to: receive electromagneticsignals during a noise detection portion; determine a noise valueindicative of a noise level that corresponds to a number of measurementsof the electromagnetic signals received during the noise detectionportion; adjust a signal detection threshold based at least in part onthe determined noise value; and determine whether any of the resonanttag elements are present in the work area based at least in part on anumber of measurements of the return signals received and the adjustedsignal detection threshold.
 10. The transponder detection device ofclaim 9, wherein the nontransitory processor-readable medium storesfurther instructions or data executable by the processor, which causethe processor to: compare a maximum value of a plurality of matchedfilter outputs with the adjusted signal detection threshold.
 11. Thetransponder detection device of claim 2, wherein the widebandinterrogation signals are centered in at least one of a 136 kHz band, a139 kHz band, a 142 kHz band, a 145 kHz band, a 148 kHz band, a 151 kHzband and a 154 kHz band.
 12. The transponder detection device of claim1, wherein each of the three coil support channels is shaped as aspherical zone of a virtual sphere.
 13. The transponder detection deviceof claim 1, further comprising a hand-held probe supporting the coilform, wherein the hand-held probe includes a housing defining a cavitysized and shaped to receive the coil form therein.
 14. The transponderdetection device of claim 13, wherein the cavity of the housing isdefined by a substantially spherical body portion, and the housingfurther comprises a handle portion coupled to the body portion.